Providing you with confidence and clarity when complications arise.
An opinion from any solicitor or barrister, no matter how senior and experienced, is just that: an opinion. It does not prevent HMRC (or any other relevant authorities) from forming their own different opinion on the correct interpretation of the relevant tax rules and legislation, and from then pursuing legal action against you based on their different opinion.
Generally speaking, the advice that you received on your tax affairs from your relevant advisor(s) is a matter for you to take up with them directly, but it will be unlikely to provide you with a defence to any potential enquiry or claim brought by HMRC. As mentioned above, if the advice that you received from your tax advisor was negligent, then you may potentially have a separate professional negligence claim against them, but you would still normally be liable to HMRC for any incorrectly unpaid tax (although your conduct is potentially something that HMRC may take into account when exercising any discretion that it has in relation to, for example, imposing penalties and interest).
Assuming that the terms for the sale and purchase of the business were set out in a formal agreement, it will be necessary as a first step to consider the scope of any tax warranties provided by the seller to the purchaser in that agreement, as these could potentially require the seller to indemnify the purchaser in respect of certain losses arising from the pre-completion actions of the seller in relation to the business’ tax affairs. However, as with any potential professional negligence claim against a tax advisor, any potential claim against a seller under a tax warranty will normally be something that you would have to pursue against them separately, and it will be unlikely to provide you with a defence to any potential enquiry or claim brought by HMRC.